Making the Frame (part 2)

March 12, 2016 Rich Leave a comment

After cutting the tenons and mortises, Jack and I did the standard fine tuning on the mortises to get the parts to fit together accurately, but without a bunch of man-handling. It was important that the mortise and tenon fit wasn’t too tight, because four joints on each end must be fit simultaneously during the glue-up, and it is very hard to seat them all if they are tight. After a few dry fits, we were ready to mark and drill the holes in the rails that receive the saddle and corner posts.

Post Holes

Now I’m not going to lie – I can tend to be a bit anal-retentive when it comes to woodworking. Feeding this natural tendency was the fact that I knew that accurate placement of the posts was critical to avoid pinching the bars between the posts. To determine the hole locations, I created an Excel spreadsheet that computed the location of each post on each of the four rails. The computed locations were distances down the length of each rail, relative the shoulder of the tenon. The only problem is that I kept screwing this up- mostly due to the four unique angles and all of the offsets involved. I would compute the locations and then mark them on the rails with jack reading off the dimensions. But when we checked them, there would be some systematic error – like I hadn’t accounted for the offset due to the pin being in the center of the rail. I think we did this three times before we got it right – argh! Both Jack and I were frustrated by this tedious process (did I mention that there were 108 holes?!)

After we did it this way, I realized that there is a much simpler approach that I would use if I ever did this again. Let me explain…

Computing the post locations relative to the left ID of the frame is straightforward (as opposed to distance down the rail). It is really just accounting for each bar and gap width. You do have to be a little careful with the offsets (i.e., edge-to-corner post, edge to first saddle pin, etc), but it is do-able with a little care. The tricky part is the angles involved and the fact that the index mark for the hole location has to be at the edge of the rail to make the drilling operation efficient. Let me clarify. Check out the photo at the top of this post. This is the setup on my drill press where we drilled the holes. Here is a zoom of the center of that photo:

Blowup of drilling operation showing the index marks

It may be hard to see in the photo, but there is a thin pencil mark on the edge of the Mahogany support rail that must be aligned with the scribed line on the steel angle jig behind the rail. The drilling process for each hole was basically to align the marks, apply a spring clamp to hold the board against the steel fence, and drill the hole. The spacing between the drill bit center and the steel fence was exactly 1/2 inch so that each hole would be precisely centered on the width of the board.

Here is a wider field of view photo of the drilling setup that may help:

Because each rail is angled, there is a small offset between the desired X location of each hole and the mark at the edge of the board. Neglecting this, or getting the offset in the wrong direction is how I kept screwing up. Also, when making the marks on each rail, it is easy to mess up, since the distance down the rail is relative to the rail center line, not the edge. This is another way I screwed up. So here is a much easier approach that occurred to me after the fact.

Rather than trying to account for this angle-dependent offset, I would do the following:

Dry fit the frame together
Compute the location of each hole relative to the left or right ID of the frame end piece (i.e., in the X direction)
Using the protractor head on a combination square, set the angle so head is against the rail and the blade is aligned with the frame end (so the blade is parallel to the Y axis)
Slide the combo square down the rail to align the blade with the desired X location (e.g., using a tape measure that measures distances form the frame end ID) computed for a given hole.
Draw a line on the top of the rail. This line will be slanted relative to the rail perpendicular.

Now you will have a slanted pencil mark at each post location. When aligning the mark on the drill press, you can not just line up the pencil mark with the index line on the steel angle block. If you do this, the hole will be offset a bit from the desired location due to the 1/2 inch thickness of the rail and the fact that the line is slanted. Rather, you will have to align the drill press index mark with the intersection point of the slanted line and the mid-point of the rail. A small right angle block could facilitate this, or you could draw an additional perpendicular line at each mark location.

Hopefully, my lesson will save you some pain, or perhaps you will have better luck with the calculations and getting all of the angles right – we finally did, but it was painful.

In the end, we got all of holes drilled, temporarily pushed all of the posts in the holes, and temporarily strung the bars with some string. Here is a photo of Jack with our assembled unit. It’s starting to look like a real instrument.

Jack couldn’t resist playing a little ditty. Here is a video of Jack playing his evolving xylophone for the very first time:

Shaping the Ends Pieces

As shown on the photos of the previous posts, the frame ends at this point were just rectangular blocks, which look pretty clunky. As previously noted, we placed the mortises so that the top of the accidental bars were at the same elevation as the top of the rectangular frame ends. This was just an aesthetic decision. We thought it would look good to extend this idea to the natural bars too, which required the frame ends to “step down” to the elevation of the natural bar tops.

To avoid square, sharp corners, we also added little ramps that connected the two elevations and rounded all of the corners. Here is a photo of the nearly finished end pieces.

Notice that we also cut some big, rectangular mortises in the bottom of each end piece. This is to accept the two legs that we had yet to build. We’ll write more about the leg and foot construction in a later post.

To smooth the sharp corners, we routed a 1/4 round-over on all of the edges and dry-fit the whole thing together to take a look. Here is the result:

Applying Finish

I chose lacquer for the frame finish. I like lacquer because it really brings out the depth in the wood but also because it drys quickly, so it is fast to build up a finish. We decided to finish the rails and end pieces prior to assembly for a few reasons. First, down at the right end of the instrument, the spacing is a little tight, so it is hard to spray finish in there. Second, there is inevitably glue squeeze out at the joints, and it is often hard to remove all of that glue prior to finishing. Any glue left behind will keep the wood from absorbing the finish which leaves unsightly “splotches.” So we put blue painters tape over the mortises and tenons and sprayed the parts with an HVLP gun. (I use a cheap $100 HVLP system from Rocker for the finish. For the price, this thing is actually pretty decent.) Here are a few photos:

It’s always fun to watch the grain pop on wood when lacquer is applied. The finish also brought out the beautiful color of the Mahogany.

After the finish dried, we glued and clamped the frame assembly. This was a bit “butt puckering” because it is a tricky to get the tenons simultaneously inserted in to the mortises before the glue dries, especially in arid New Mexico where the humidity is so low. Here are few photos of the glue-up:

All that was left was to glue the posts into the rails. Each of the post holes was drilled with a brad-point bit to a fixed depth. This gave a nice square bottom to each hole that ensured that all of the pins would have the same elevation. The pins were snug in the hole, but over time may have wiggled out, or at least rotated, so I decided to drop a bit of glue in the bottom of each hole to lock the pin into place. I carefully inserted the glue into each hole using a toothpick and letting the glue drip in. This was slow going (did I mention that there are 108 holes,) so it took a while. Here is a photo:

Here are a couple of photos of the completed frame:

And then came the moment of truth – Jack and I strung the xylophone bars on some brown para-cord, attached the springs, and hung the bars. Pretty cool – we now had a fully functional instrument, minus legs and resonator tubes. Here are some photos of the finished product:

It had been a long time coming, but we finally had an instrument! Jack and I moved this up to his bedroom at this point, so he could mess around with it, and to get it out of the garage so we could start working on the resonator tubes. More on that in the next post.

We’ll leave you with Jack playing a little song in his bedroom.

Xylophone

Making the Frame (part 1)

March 5, 2016 Rich Leave a comment

The first step in building the frame was to determine the total width between the two frame ends (i.e., the ID of the frame width). This was primarily dictated by the bar width and the gaps between the bars. As we’ve described, each of the bars was 1.5 inches wide. The width of the saddle pin with the surgical tubing attached was just about ¼ inch. We messed around a little and found that an extra 1/16 of an inch was about right to include for additional spacing around the pins, yielding a total gap between each pair of bars of 5/16 of an inch.

Next, we had to figure out how much space to leave for the corner posts and springs that are situated between the end bars and the frame. We determined this spacing empirically by laying out the springs and the corner posts on a table top and adjusted the spacing until we had enough rough to comfortably reach the springs between the outside bar end and the inside edge of the frame end. We found that 3 cm was about right for this spacing.

Now we had enough information to compute the total distance between the frame ends. For those of you who have gotten this far, I probably don’t have to tell you that xylophone bars are laid out like piano keys where the white natural keys are toward the player and the black accidental keys are toward the rear. But just to make it clear, here is a rough layout of my 44 bars:

As you can see, the natural bars (at the bottom of the photo) determine the total width of the instrument, since the total width for these is greater than for the accidental bars. So the total inside dimension of the instrument is becomes

ID = (3 cm) + (26 bars)*(1.5 inches) + (25 gaps)*(5/16 inches) + (3 cm)

ID = 124.904 cm

The bar width and gap width define the X location (i.e. left/right) of each natural bar, and the pins are of course just centered between each bar. The X center position of each accidental bar just lines up with each natural bar gap center. I had a big complicated Excel spreadsheet that computed all of these dimensions, but this turned out to be more complicated than it needed to be, so I won’t confuse you by including it. I’m sure you can do a bit of arithmetic and determine the bar locations…

Dimensionally, we also had to determine the Y spacing (i.e., fore/aft) between the rails. Recall that the angles of the bar support rails was previously determined by lining up yellow thread suspended by posts with the average node locations. With the 124.9 cm ID spacing drawn on a large piece of construction paper, we simply marked the physical locations of the thread intersection with the inside edges of the frame ends on the paper for both the natural and accidental bars. We were careful to allow for clearance necessary to ensure that the aft ends of the natural bars were about ¼ inch away from the front accidental support rail. This established the center lines for each of the four angled support rails. Here are a couple of scrappy drawings that may help to illustrate all of this.

In addition to the photo at the top of this page, here is another picture of the rails attached to the frame ends to illustrate the geometry:

Frame showing elevated accidental support rails in the foreground

The only dimensioning left was to determine the Z spacing (i.e., up/down) of the accidental bars relative to the natural bars. You can see in the photo above that the rails for the accidental bars are elevated above the natural bars. Elevating the accidental bars minimizes the fore/aft spacing of the natural and accidental bars by allowing the accidental bars to overlap the natural bars. The vertical gap between the natural and accidental bars was sent to ½ inch to ensure that the bars would not touch even if the string was loose and the bars sagged.

Laying Out the Frame Ends

We built the frame ends out of 8/4 maple (after dimensioning the lumber, the thickness was about 1.75 inches) that had a bit of figure to it. We wanted these to be beefy, because we knew that it needed to keep the support rails from racking, and it needed to support bolt-on legs. However, at this point we weren’t quite sure what exact shape we wanted for the frame ends but did know that we wanted the top of them to be roughly level with the top of the suspended accidental bars. So we oversized them prior to cutting the mortises that would receive the rail tenons. We had to figure in the total height of the bar above the suspension rail, which is of course a function of the saddle posts that hold up the bars. So we drew the following picture to try to get all of the dimensions right. Again, this picture a pretty scrappy picture, but at least has all of the dimensions annotated.

When laying out the mortise locations for the Maple frame ends, we indexed everything from the top and fore/aft center of the rectangular frame end pieces. The rails themselves were made from 1×2.5 Mahogany stock. We chose Mahogany because it is dimensionally stable (i.e., unlikely to bow,) because we thought it would look good with the Maple and Rosewood and because we had it on hand. For strength, we wanted the largest tenons that we could reasonably make. The largest chisel for my tenoning jig is ½ inch, so that established the width of the tenons. To keep the shoulder consistent at ¼ inch, we made the tenons ½ x 2 inches.

To keep the layout as simple as possible, we centered each of the support pins on the midpoint (in the thickness direction) of the Mahogany support rails, so the center line on these rails had to meet up with the marked locations on the frame ends accurately or the suspension strings wouldn’t pass through the center of the bar holes. So getting the mortises accurately placed in the Maple end frame pieces was important. Here is a few photos of the mortised frame ends:

Zoom of 2.5x1/2 inch mortise — Zoom of 2.5×1/2 inch mortise

With the mortises cut, we had to make the tenons on the ends of the Mahogany support rails. What made this somewhat tricky was that these tenons had to be angled, relative tot he long axis of the rails. Angled tenons are always a bit tricky, but this was complicated by the fact that each of the four tenons for a given end were at different angles – a lot to keep track of.

I cut these angled tenons using a delta tenoning jig on my table saw, with Jack on quality control (i.e., making sure I got the correct angles and in the correct directions). I don’t have any photos of this, but I’m sure there is lots of info on the web that describe cutting angled tenons. Personally, I think the “cheek” cuts on the shoulders is the hardest part.

Here are a few photos of the final tenons:

Next up

The tenons and mortises were cut, but we still had to mark and drill all of the holes for the posts and had to shape the end frames. We’ll discuss that, and a few other odds and ends, in the next post.

Xylophone

Designing the Frame

March 5, 2016 Rich Leave a comment

The previous work that we had done to establish the suspension hole locations provided precise angles for the suspension rails. These angles, coupled with the bar lengths, established the fore/aft spacing of the natural and accidental bars. We decided to use 1 inch thick rails, so we had to just ensure that all of the aft ends of all of the natural bars had sufficient spacing from the front accidental support rail. We choose to leave 1/4 inch spacing between the natural bars and the support rail just to allow us a little wiggle room. Constructing the xylophone frame, including the rails that support the bars and the two end pieces, was pretty straight-forward woodworking, but we had to put some thought into the suspension posts and how the resonator tubes would be mounted.

Here are some practical matters that had to be addressed that might affect the frame design and therefore had to be addressed first:

What to use for the posts that support the suspension strings?
The diameter of the resonator tubes?
How to support the resonator tubes?

The question of posts was important, because, depending on the thickness, it might have a bearing on the bar spacing. The post height might also affect the frame design, so we needed to figure that what our posts were going to be before building the frame.

There was a similar issue for the resonator tubes – the diameter might drive the spacing of the frame. Although this seemed like less of a concern than the post selection, I had learned from my previous woodworking projects that you always select hardware first (e.g., it is easier to build a box around available hinges than to find hinges that fit a project you’ve already built). So it seemed smart to figure out what material was available and cost effective.

I wasn’t as concerned about the last question, how to mount the tubes, but it seemed like giving this some thought could keep me out of trouble down the road.

The Posts

I anguished over what to use for posts. Most commercial xylophones that I found had posts like the ones shown in the image at the top of this page. I saw a few variations, like posts with a through-hole rather than a “saddle” to support the string, but all of the posts were similar and were cut from flat metal. In addition to the post itself, most included a rubber sleeve to keep the bars from buzzing against the metal during play. I had found a source of replacement posts made for Musser-brand instruments here, but they’re about 90 cents which doesn’t sound bad until you realize that I need 108 for the instrument! I also needed the rubber sleeves, which were sold by the same vendor for about a buck a piece – ouch! So I wracked my brain trying to determine an easy way to build them. Dr Entwistle weighed in too, but every idea we came up with (e.g., brass bolts with a bit of machining) was either nearly as expensive or required a bunch of per-post labor. Now I am pretty patient when it comes to repetitive tasks (hey, I built a xylophone, right!), but hand machining 108 posts was more than I could stomach.

So at the end of the day, I bit the bullet and just bought the posts from the link above. I also bought some springs that tension the suspension strings and some really nice end posts that support the tension load of the strings at the corners. It was hard to tell from the photos on the vendor website, but when I got these I was actually pretty pleased with the quality. Here are a couple of photos of the “saddle posts” and the corner posts:

Musser "saddle" posts — Musser “saddle” posts

The springs were nothing special, but were inexpensive, so I went ahead and bought them from the same site. Here was an invoice of the parts:

Actually, you will notice that I messed up and only ordered 100 posts – argh! I ended up ordering another 10 from a different vendor that had cheaper shipping for small orders.

The only thing left was the rubber bumper material – I wasn’t so keen on giving Musser another hundred bucks for a bunch of little rubber pieces. I had some surgical tubing around for another project, and I found that with a little soapy water for lubrication, I could slide it over the posts for a perfect fit. The only downside was that it was that standard tan color that is typical of surgical tubing. However, I found some black tubing of the same size from this source. This was only $10.95 (with free shipping) for 10 feet, which was more than enough. Sweet, that’s about a $100 savings! It looks great on the post too. Check this blow up of the posts with the surgical tubing and the corner posts.

Zoomed image of my posts with the rubber jacket

Resonator Tube Material Selection

We really, really, really wanted to make the resonator tubes out of brass. Polished brass just looks so classy, and we were trying to make an instrument that looked as good as it sounded. However, the cheapest price I could find for brass was about $13 per foot. Considering that we needed about 20 feet (more about the resonator tube lengths in a later post,) that was a pretty expensive option. We also considered that brass is pretty heavy, so the supports would have to be beefy enough to support the weight. At the end of the day, we compromised and decided to make the tubes out of aluminum – not quite as sexy as brass, but after applying a brushed finish and some lacquer, they looked pretty good.

We just had to figure out the diameter. Our rosewood bars are 1.5 inches wide, and we planned to space them about 1/4 apart. So the tubes could be up to 1.75 inches in diameter. However, the paper by Bork (cited on a previous post) suggested that resonator “cross-talk” with neighboring notes could be an issue if the bars were too close together. This potential issue would be worse for the B-C and E-F bars, which are only a semitone apart and adjacent. However, we also considered that a diameter of 1.75 inches would be convenient from a mounting standpoint, because the bars would be butted together, which might ease assembly and aesthetics.

In the end, the solution was driven by the available materials; after a local supplier gave me a quote of $350 for 20 ft of aluminum tubing (!!), I started looking online. Ultimately, I bought 1.5 inch tubing with 1/16 walls. This was about $15 per 4 foot length from Speedy Metals, which is a very reasonable price. (In general Speedy Metals is a great vendor with lots of selection and prices – I love this place!) I calculated that I needed 5 pieces, but bought 6 just in case. Speedy Metals also had 1.75 inch tubing, but only in 1/8 inch wall, which was a lot more expensive and overkill for this application.

Mounting the Resonator Tubes

All of the xylophones that I saw connected the tubes together to form an assembly and then hung them in some fashion from the frame ends. I decided to attach wood cleats to the frame ends to support the resonator tube assemblies. You’ll see more of this in a later post, but I used 1×1/8 aluminum flat stock to tie all of the tubes together. The aluminum is 6061, which is pretty stiff, but bendable; this was important because I had to bend the these support rails at the end where the wood support rails converged.

Here is a snapshot of the invoice for all of the aluminum:

Next Up

Chronologically, the next step that Jack and I performed on the xylophone was the construction of the resonator tubes. However, that included a bit more research and math, so to mix things up a little I will discuss the frame construction in the next post. Finally a little wood working!

SuperMediocre

Monthly Archives: March 2016